Receiver gain control circuits



NOV. 14, 1.939. K, HAGENHAUS 2.179.928

RECEIVER GAIN CONTROL CIRCUITS f Filed sept. 16, 193e /VD FILTER INVENTOR' KURT ),HAGENHAUS ATTORNEY Patented Nov. 14, 1939 UNITED STATES RECEIVER GAIN CONTROL CIRCUITS Kurt Hagenhaus, Berlin-Siemensstadt, Germany,

assignor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a

corporation of Germany Application September 16, 1936, Serial No. 100,970

In G

3 Claims.

My present invention relates to a radio frequency receiver with acoustic intensity range regulation means.

The intensity of reproduction is compressed, for instance, in broadcast apparatus in order that the transmitter may not be overloaded during loud passages. It is known that the intensity may be expanded again in the receiver in order that sound reproduction fidelity may be insured which will Icome more closely to the original production.

Now, if such intensity regulation is to be accomplished in the receiver by action upon the radio frequency amplifier only, the so-called retrogressive regulation may be taken into consideration. If, then, the regulator potential obtained by rectification of the audio energy is fed to the radio amplifier to be governed, there arises the risk of an lundesirable over-regulation. It will be noted that with increase of the audio, the amplification or gain of the radio amplifier is raised, and this results in a further increase of the audio in the sense of the desired acoustic regulation. The consequence is that also the control, or regulator, potential experiences a rise, and this results in the radio amplifier gain being raised still further. In other words, there is a real danger and risk for the amplifier being overshot, or overloaded.

Now, according to this invention the said drawback is avoided in that regulation is effected with a voltage in the radio amplifier corresponding to the modulation percentage. Excessive or overregulation, above referred to, will then no longer be able to happen, seeing that by an increase in the radio amplification the ratio between the audio amplitude and the radio amplitude (modulation percentage) is not infiuenced.

The practical application of the basic idea of this invention shall be described in more detail in what follows by reference to the two annexed figures wherein Figs. 1 and 2 show different embodiments of the invention.

Referring to Fig. 1, it will be seen that following the radio amplifier stage I-IFi the regulating rectifier Gs is connected for fading adjustment or compensation. The regulator potentials, after removal of the audio energy by filters, are brought to act upon the radio stages HFi and HFz. Following the receiving rectifier or detector GE, the direct current component corresponding to the signal carrier amplitude is fed to one coil of a crossed-coil type of instrument K, While the direct current component corresponding to the audio amplitude, which is ermany September 27, 1935 (Cl. Z50-20) obtained in the rectifier GD, is impressed upon the other coil of the same instrument. The movable slide K1 of the instrument slides over a potentiometer P, which is connected across a source of direct current B. Thus, by way of the line L a regulation voltage, which corresponds to the modulation percentage, will be impressed upon the radio amplifiers. The audio amplifier is indicated at NF.

Fig. 2 shows an arrangement which operates without any mechanical means. In this instance, fading compensator potential isk impressed upon the radio amplifier HFi by way of the rectifier Gs. The radio energy further, is rectified in rectifier G1 so that across the terminals of the condenser C, which shorts only radio energy, there will prevail a direct current and audio voltage. Resistance W is a normal resistance, whereas H denotes a hot conductor (i. e., a resistance with a negative temperature coefficient), say, a uranium dioxide resistance, across which is acting a constant potential in spite of fluctuating currents. inasmuch as the said hot conductor, as a result of its thermal inertia, has an adjusting period amounting to several seconds or over, it follows that the audio energy will not be smoothed, but will persist or be preserved. In this arrangement there is thus obtained across the hot conductor I-I an audio potential which will correspond to the percentage modulation.

The audio voltage arising across I-I is rectified in the rectifier G2, and the direct current voltage obtained across resistance R is used for the regulation of the acoustic intensity range, or volume ratio.

The present invention, as will be obvious, is not confined to the two instances hereinbefore cited; in fact, recourse could be had to any arrangement which will furnish a regulator Voltage corresponding to the modulation percentage. It would, also, be feasible to effect regulation of the volume ratio in a radio stage which is not subject tofading compensation.

What is claimed is:

1. A method of expanding the volume range of a receiver of the type including at least one radio frequency amplifier tube, which includes detecting amplified modulated carrier energy to provide a direct current whose amplitude is proportional to carrier amplitude variation, rectifying the modulation voltage component of the detected carrier energy, controlling the gain of the amplifier tube in an increasing sense in response to both said rectified component and said direct current whereby the gain of said amplifier is dependent on the degree of modulation of the said carrier, and additionally automatically regulating the amplier gain in accordance with carrier amplitude variation.

2. A radio receiver including at least a high frequency amplifier, a demodulator and an audio utilization network, automatic volume control means for controlling the gain of the amplifier in response to received carrier amplitude variations, automatic volurne expansion means for said receiver comprising means for rectifying the audio component of demodulated carrier energy, and additional means, responsive to the joint action of the rectied audio component and the direct current component of said demodulated carrier energy, for varying the signal transmission eiciency through at least one of said receiver networks.

3. In combination, in a radio receiver of the type including a high frequency amplifier, an automatic volume control circuit responsive to carrier amplitude increase for varying the amplier gain in a decreasing sense, lan automatic volume expansion circuit, responsive to the degree of modulation of received carrier energy, for varying the amplifier gain in an increasing sense, said expansion circuit including a rectifier of the carrier energy, a second rectifier of the modulation component of the rectified carrier energy, and means responsive to the unidirectional current outputs of both rectiers.

KURT HAGENHAUS. 

